The present invention relates to a thrust converter for driving a press-working machine or a chucking apparatus for holding a workpiece through use of a lathe, to a method of controlling the thrust converter, and to a controller for controlling the thrust converter.
A press-working machine or a drive machine having a chucking mechanism for holding a workpiece through use of a machine tool or the like often employs thrust induced by a hydraulic cylinder or a pneumatic cylinder.
FIG. 13 is a fragmentary longitudinal cross-sectional view showing one example of a related-art press-working machine using a hydraulic cylinder as a drive source. A hydraulic cylinder 51 is secured on a stand 52 byway of a cylinder bracket 50 and is connected to a hydraulic system 53 via a pipe 54. A push-pull rod 56 is fixed to a load-side extremity of a piston 55 of the hydraulic cylinder 51. A press punch 57 matching a geometry to be machined is attached to the extremity of the push-pull rod 56. A work table 58 is situated in a lower position within the stand 52, and a workpiece 59 is fixedly placed on the work table 58. The push-pull rod 56 is guided by the cylinder bracket 50 by way of a slide guide 60 so as to be slidable in the axial direction.
In such a related-art press-working machine, the piston 55 of the hydraulic cylinder 51 is reciprocated by means of oil supplied from the hydraulic system 53 by way of the pipe 54. By means of thrusting action of the push-pull rod 56 fixed to the piston 55, the press punch 57 is pushed, to thereby press, into a desired geometry, the workpiece 59 fixedly placed on the work table 58.
FIG. 14 is a fragmentary transverse cross-sectional view showing one example of related-art chucking apparatus using a hydraulic cylinder as a chuck drive source. A rotary hydraulic cylinder 64 is supported by a cylinder cover 66 via shaft bearings 65a and 65b. A rear extremity of a main spindle 70 is secured on a load-side extremity of the rotary hydraulic cylinder 64 via an adapter 72a. 
A chuck 71 is secured on the front extremity of the main spindle 70 via an adapter 72b. A draw bar 73 is inserted into an internal hollow spindle core of the main spindle 70, and the extremity of the draw bar 73 is engaged with chuck claws 74 via an operation conversion mechanism 75. The operation conversion mechanism 75 converts axial operation of the draw bar 73 into radial operation of the chuck claws 74 by means of a cam lever or a taper.
The rear extremity of the draw bar 73 is secured to the load-side extremity of a piston 55 of the rotary hydraulic cylinder 64.
In the related-art chuck drive system using a hydraulic cylinder as a chuck drive source, oil is supplied to the rotary hydraulic cylinder 64 from a hydraulic system 53 via a pipe 54, thereby reciprocating the piston 55. The axial operation of the draw bar 73 is converted into a radial operation of the chuck claws 74, thereby causing the chuck 71 to hold a workpiece 67.
After the chuck claws 74 have held the workpiece 67, a main spindle motor 76 is rotated, thereby cutting the workpiece 67 and causing rotation of the main spindle 70, the draw bar 73, the chuck 71, the operation conversion mechanism 75, the rotary hydraulic cylinder 64, the piston 55, the workpiece 67, and the adapters 72a and 72b, thereby machining the workpiece 67.
In the related-art examples, a hydraulic cylinder is used for a press-working machine or a chucking apparatus. The same also applies to a case where a pneumatic cylinder is employed.
Another related-art example is a chucking apparatus using an electric motor as a chuck drive source described in Japanese Patent Application Laid-Open No. 34708/1987.
The chucking apparatus described in Japanese Patent Application Laid-Open No. 34708/1987 employs an electric motor as a chuck drive source. Drive force of the electric motor is amplified by a decelerator, and the thus-amplified drive force is transmitted to the chucking apparatus main unit. The chuck is closed by means of the thus-amplified drive force, thereby holding a workpiece.
At the time of machining operation, the workpiece is machined while a draw bar drive system is separated from a rotary system of the main spindle by means of an electromagnetic clutch.
In a press-working system or a chucking apparatus employing a related-art hydraulic cylinder or pneumatic cylinder, thrust is determined by the pressure which a hydraulic or pneumatic system can produce as well as by the diameter of the cylinder. When greater thrust is required, the pressure and/or the diameter must be changed correspondingly, thereby adding to costs.
Some decelerators employ gears as a torque amplification (or torque reduction) mechanism. Such a decelerator usually amplifies (or reduces) a rotational input and outputs as a rotational output. In order to amplify (or reduce) an axial input (or thrust) and output an axial output (thrust), mechanical components such as various gears must be combined together, thereby rendering the chucking apparatus bulky. Reactive force is exerted on a bearing which supports gears in a rotatable manner, thereby shortening the life of the decelerator. For this reason, a desire exists for a low-cost, compact, long-life thrust converter of simple construction which can amplify (reduce) an axial input (thrust) and output the thus-amplified axial input as an axial output (thrust).
Employment of a decelerator adopting a gear mechanism for amplifying the rotation torque of a motor, as in, for example, a chucking apparatus described in Japanese Patent Application Laid-Open No. 34708/1987, requires an electromagnetic clutch for separating a draw bar drive system from a main spindle rotation system during machining of a workpiece. Thus, the chucking apparatus presents a problem of an increase in the number of components, thereby adding to costs.
In the electromagnetic chucking apparatus, a workpiece is held by imparting axial thrust to a draw bar. During machining of a workpiece, a bearing which rotatably supports the draw bar receives all reaction force of axial thrust. Hence, an increase in the rotational speed of the main spindle or an increase in holding force due to an increase in axial thrust of a draw bar poses problems of drastically shortening the life of a bearing.
The present invention provides a thrust converter comprising:
reciprocating movement means;
reciprocation-rotation conversion means for converting reciprocating movement of the reciprocation movement means into rotational movement;
rotation-reciprocation conversion means for converting rotational movement of the reciprocation-rotation conversion means into reciprocating movement; and
reaction-force receiving means for supporting reaction force of reciprocating movement of the rotation-reciprocation conversion means.
Hence, thrust imparted to the reciprocation movement means can be imparted to a load while being amplified or reduced, through employment of a compact and simple construction. So long as the thrust converter is applied to a press-working machine or a chuck drive machine, thereby providing a useful novel thrust converter.
Preferably, the reciprocation movement means, the reciprocation-rotation conversion means, the rotation-reciprocation conversion means, and the reaction-force receiving means are aligned in one line, and a through hole is formed so as to pass through the center axes thereof.
Hence, there can be provided a thrust converter which can be applied to a lathe chuck for machining long materials.
Preferably, the reciprocation-rotation converter means comprises a first screw member to which axial thrust is imparted by the reciprocation movement means, a second screw member to be screw-engaged with the first screw member, and a first detent section for locking the first screw member so as to restrict movement to only an axial direction; the rotation-reciprocation conversion means comprises a screw section provided on the second screw member in a position different from the location of a screw section to be screw-engaged with the first screw member, a third screw member to be screw-engaged with the screw section, and a second detent section for locking the third screw member so as to restrict movement to only an axial direction; and the reaction-force receiving means comprises a substrate, the second screw member, and a first shaft bearing for supporting the second screw member on the substrate so as to allow rotation and to prohibit axial movement.
The majority of the constituent elements can be formed from screw members, and hence there can be provided a low-cost thrust converter having superior productivity.
Preferably, the first screw member is supported by the reciprocation movement means by way of a second shaft bearing so as to be rotatable.
Hence, the reciprocation movement means, the reciprocation-rotation conversion means, the rotation-reciprocation conversion means, and reaction-force receiving means can be separated from each other in a rotating direction with use of simple components. There can be provided a thrust converter applicable to a lathe chucking apparatus whose load rotates at high speed.
Preferably, the reciprocation movement means comprises a motor, and motor rotation-reciprocation conversion means for converting rotating movement of a shaft of the motor into reciprocating movement.
There can be provided a thrust converter which has a good maintenance characteristic and which enables easy non-stage control of thrust to be output to a load with a simple construction.
Preferably, the reciprocation movement means comprises a motor, a fourth screw member provided on a load-side extremity of a shaft of the motor, a fifth screw member to be screw-engaged with the fourth screw member, a third detent section for locking the fifth screw member so as to restrict movement to only an axial direction, and motor rotation-reciprocation conversion means for converting the rotating movement of the shaft of the motor into reciprocating movement; the reciprocation-rotation conversion means comprises a first screw member supported by the fifth screw member so as to allow rotation and to prohibit axial movement by way of a second shaft bearing, a second screw member to be screw-engaged with the first screw member, and a first detent section for locking the first screw member so as to restrict movement to only the axial direction; the rotation-reciprocation conversion means comprises a screw section provided on the second screw member in a position different from the location of a screw section to be screw-engaged with the first screw member, a third screw member to be screw-engaged with the screw section, and a second detent section for locking the third screw member so as to restrict movement to only an axial direction; and the reaction-force receiving means comprises a substrate, the second screw member, and a first shaft bearing for supporting the second screw member on the substrate so as to allow rotation and to prohibit axial movement.
The majority of the constituent elements can be formed from screw members, and hence there can be provided a low-cost thrust converter having superior productivity. Further, there can be provided a thrust converter which has a good maintenance characteristic and which enables easy non-stage control of thrust to be output to a load with a simple construction.
Preferably, the second detent section for locking the third screw member so as to restrict movement to only an axial direction is interposed between the third screw member and a first screw member.
There can be provided a thrust converter having a shorter axial dimension.
Preferably, screw lead of the first screw member and screw lead of a second screw member to be screw-engaged with the first screw member are greater than screw lead of a screw section provided on the second screw member in a position different from the location of a screw section to be screw-engaged with the first screw member and greater than screw lead of a third screw member to be screw-engaged with the screw section.
There can be provided a thrust converter which can produce great thrust on a load with a simple construction and a small thrust drive source and which can make the unit of amplification minute.
Preferably, screw lead of the first screw member and screw lead of a second screw member to be screw-engaged with the first screw member are smaller than screw lead of a screw section provided on the second screw member in a position different from the location of a screw section to be screw-engaged with the first screw member and smaller than screw lead of a third screw member to be screw-engaged with the screw section.
There can be provided a thrust converter which can impart thrust to a load while reducing the load with a simple construction and a small thrust drive source and which can make the unit of amplification minute.
Preferably, provided that a screw lead angle between a screw section which is formed on the second screw member in a location different from that of a screw section to be screw-engaged with the first screw member and a third screw member to be screw-engaged with the screw section is taken as xcex2 and a coefficient of friction of a screw is taken as xcexc, a screw is formed so as to assume a relationship tan xcex2 less than xcexc.
Although rotational torque can be converted into thrust, thrust cannot be converted into rotational torque. Hence, loosening of the third screw member stemming from counteracting thrust imposed by a load can be prevented. After given thrust has been imparted to a load, thrust of the reciprocation movement means can be interrupted, thereby realizing energy saving. Since the reciprocation movement means and the reciprocation-rotation conversion means are separated from each other in the rotating direction. There can be provided a thrust converter, wherein, when a second bearing is interposed between the reciprocation movement means and the reciprocation-rotation conversion means, no thrust load is imposed on the second bearing, thus lengthening the life of a shaft bearing.
Preferably, a main spindle shaft of a chucking apparatus corresponding to the substrate is secured to a mount frame fixed to a load-side bracket of a motor by way of a third bearing so as to be rotatable and to not be capable of axial movement.
There can be provided a thrust converter which can be replaced with a chucking apparatus employing related-art hydraulic or pneumatic cylinder.
Preferably, the second bearing is constituted of a double bearing.
Hence, there can be provided a thrust converter which can reduce load exerted in the direction of thrust one-half, thereby lengthening the life of a shaft bearing.
Preferably, a motor whose torque can be controlled through current control is used as the motor, and constant thrust is produced by constant control of the current to the motor.
There can be produced a thrust converter which can produce given thrust at all times.
The present invention provides a method of controlling a thrust converter, wherein a motor whose torque and positions can be controlled through current control is used as the motor; and wherein the position of the motor is controlled until the motor moves to a predetermined position, and torque of the motor is controlled. When the thrust converter is applied to a lathe chucking apparatus, there can be provided a thrust converter capable of increasing chucking operation.
Preferably, the present invention provides a method of controlling the thus converted device, wherein, on the basis of the moving state of an external driver source other than the drive source of the thrust converter, there is computed the amount of correction to be used for correcting the position or torque of a motor of the thrust converter. The position or torque of the motor of the thrust converter on the basis of the thus-computed amount of correction.
Hence, application of mechanical disturbance to the thrust converter can be obviated. Hence, there can be provided a highly-precise thrust converter. For instance, when a chucking apparatus employs the thrust converter, disturbance due to centrifugal force can be eliminated, thereby enabling generation of appropriate holding force at all times.
Preferably, the present invention provides a method of controlling the thus converted device, wherein, on the basis of the temperature of a machine having the thrust converter provided thereon, the amount of correction to be used for correcting the position of a motor of the thrust converter is computed or read from memory. The position of the motor of the thrust converter is corrected on the basis of the amount of correction.
Application of thermal disturbance to the thrust converter can be obviated without addition of a special device. Hence, there can be provided a high-precision thrust converter. For instance, if a chucking apparatus adopts the thrust converter, thermal disturbance can be eliminated, thereby enabling constant generation of appropriate holding force.
Preferably, there are provided an input section for entering a moving status of an external drive source other than a drive source of the thrust converter; computation means for computing the amount of correction used for correcting the position or torque of a motor of the thrust converter on the basis of the moving status entered by way of the input section; and correction means for correcting the position or torque of the motor of the thrust converter on the basis of the computed amount of correction.
Application of thermal disturbance to the thrust converter can be obviated without addition of a special device. Hence, there can be provided a high-precision thrust converter. For instance, if a chucking apparatus adopts the thrust converter, thermal disturbance can be eliminated, thereby enabling constant generation of appropriate holding force.
Preferably, there are provided an input section for entering the temperature of a machine having provided thereon the thrust converter;
means for computing the amount of correction required for correcting the position of a motor of the thrust converter or reading the amount of correction from memory; and
correction means for correcting the position of the motor of the thrust converter in accordance with the amount of correction. Application of thermal disturbance to the thrust converter can be obviated without addition of a special device. Hence, there can be provided a high-precision thrust converter. For instance, if a chucking apparatus adopts the thrust converter, thermal disturbance can be eliminated, thereby enabling constant generation of appropriate holding force.
Preferably, there are provided a manual instruction device for inputting a positional instruction to a motor whose torque and position can be controlled;
control means for controlling the position and torque of the motor; and
changeover means for which operates the motor through position control on the basis of a difference when a difference between the positional instruction and the current position is lower than a predetermined value and changes the motor to torque control when the difference between the positional instruction and the current position exceeds the predetermined value.
After the thrust converter has been constrained mechanically, thrust adjustment can be effected readily manually. When the thrust converter is applied to a lathe chucking apparatus, the status of the chucking apparatus shifts from position control to torque control by means of an operator entering only a position instruction. The operator can be effect an appropriate chuck opening/closing operation without consideration of statuses of the chuck opening and closing states.
Preferably, the changeover means comprises: current limit means for limiting a current instruction to be sent to the motor; and means which sets a limit current value of the current limit means so as to become greater than a current instruction value based on a difference when a difference between the positional instruction and the current position is lower than a predetermined value and which sets the limit current value of the current limit means so as to become smaller than the current instruction value based on a difference when a difference between the positional instruction and the current position exceeds the predetermined value.
After the thrust converter has been constrained mechanically, thrust adjustment can be effected readily manually. Adjustment of thrust can be effected without changing the gain of a feedback loop, thereby preventing occurrence of unstable control operation. When the thrust converter is applied to a lathe chucking apparatus, the status of the chucking apparatus shifts from position control to torque control by means of an operator entering only a position instruction. The operator can be effect an appropriate chuck opening/closing operation without consideration of statuses of the chuck opening and closing states.
Preferably, there are provided an input section for entering a correction value to be used for correcting a mechanical positional error of the thrust converter;
storage means for storing the correction value entered by way of the input means; and correction means for correcting the mechanical positional error of the thrust converter on the basis of the correction value stored in the storage means.
As a result, the positional accuracy of the thrust converter can be improved without being affected by the accuracy of a rotary sensor mounted on a motor or by the accuracy of the mechanism of the thrust converter. Hence, there can be provided a high-precision thrust converter through use of low-cost components and while saving costs.